Ground-level ozone

Seasonal average vertical columns of tropospheric ozone in Dobson units over the period 1979 to 2000. In June to August, photochemical ozone production causes very high concentrations over the East Coast of the US and China.

Ground-level ozone (O3), also known as surface-level ozone and tropospheric ozone, is a trace gas in the troposphere (the lowest level of the Earth's atmosphere), with an average concentration of 20–30 parts per billion by volume (ppbv), with close to 100 ppbv in polluted areas.[1][2] Ozone is also an important constituent of the stratosphere, where the ozone layer (2 to 8 parts per million ozone) exists which is located between 10 and 50 kilometers above the Earth's surface.[3] The troposphere extends from the ground up to a variable height of approximately 14 kilometers above sea level. Ozone is least concentrated in the ground layer (or planetary boundary layer) of the troposphere. Ground-level or tropospheric ozone is created by chemical reactions between NOx gases (oxides of nitrogen produced by combustion) and volatile organic compounds (VOCs). The combination of these chemicals in the presence of sunlight form ozone. Its concentration increases as height above sea level increases, with a maximum concentration at the tropopause.[4] About 90% of total ozone in the atmosphere is in the stratosphere, and 10% is in the troposphere.[5] Although tropospheric ozone is less concentrated than stratospheric ozone, it is of concern because of its health effects.[6] Ozone in the troposphere is considered a greenhouse gas, and may contribute to global warming.[4][6]

Photochemical and chemical reactions involving ozone drive many of the chemical processes that occur in the troposphere by day and by night. At abnormally high concentrations (the largest source being emissions from combustion of fossil fuels), it is a pollutant, and a constituent of smog.[7][6] Its levels have increased significantly since the industrial revolution, as NOx gasses and VOCs are some of the byproducts of combustion.[8] With more heat and sunlight in the summer months, more ozone is formed which is why regions often experience higher levels of pollution in the summer months.[9] Although the same molecule, ground-level ozone can be harmful to human health, unlike stratospheric ozone that protects the earth from excess UV radiation.[8]

Photolysis of ozone occurs at wavelengths below approximately 310–320 nanometres.[10][11] This reaction initiates a chain of chemical reactions that remove carbon monoxide, methane, and other hydrocarbons from the atmosphere via oxidation. Therefore, the concentration of tropospheric ozone affects how long these compounds remain in the air. If the oxidation of carbon monoxide or methane occur in the presence of nitrogen monoxide (NO), this chain of reactions has a net product of ozone added to the system.[2][6]

  1. ^ Warneck, Peter (1999). Chemistry of The Natural Atmosphere. Academic Press. ISBN 9780080529066.
  2. ^ a b "8.2 Tropospheric ozone". elte.prompt.hu. Retrieved 2018-11-12.
  3. ^ Department for Environment, Food and Rural Affairs (Defra) webmaster@defra gsi gov uk. "What is Stratospheric Ozone?- Defra, UK". uk-air.defra.gov.uk. Retrieved 2019-10-26.
  4. ^ a b "Nasa Ozone Watch: Ozone facts". ozonewatch.gsfc.nasa.gov. Retrieved 2018-11-12.
  5. ^ Fahey, David W. (2011). Twenty questions and answers about the ozone layer 2010 update: scientific assessment of ozone depletion 2010 (PDF). Hegglin, Michaela I., United States. National Oceanic and Atmospheric Administration., United States. National Aeronautics and Space Administration., United Nations Environment Programme., World Meteorological Organization., European Commission. Geneva, Switzerland: World Meteorological Organisation. ISBN 978-9966-7319-4-4. OCLC 770711102.
  6. ^ a b c d "Ozone in the Troposphere | UCAR Center for Science Education". scied.ucar.edu. Retrieved 2018-11-12.
  7. ^ "Tropospheric ozone | Climate & Clean Air Coalition". ccacoalition.org. Retrieved 2018-11-12.
  8. ^ a b US EPA, OAR (2015-05-29). "Ground-level Ozone Basics". US EPA. Retrieved 2019-10-26.
  9. ^ Bloomer, Bryan J.; Stehr, Jeffrey W.; Piety, Charles A.; Salawitch, Ross J.; Dickerson, Russell R. (2009). "Observed relationships of ozone air pollution with temperature and emissions". Geophysical Research Letters. 36 (9). doi:10.1029/2009GL037308. ISSN 1944-8007. Retrieved 2024-01-03.
  10. ^ Taniguchi, Nori; Takahashi, Kenshi; Matsumi, Yutaka (2000). "Photodissociation of O3around 309 nm". The Journal of Physical Chemistry A. 104 (39): 8936–8944. Bibcode:2000JPCA..104.8936T. doi:10.1021/jp001706i. ISSN 1089-5639.
  11. ^ Reeves, Claire E.; Penkett, Stuart A.; Bauguitte, Stephane; Law, Kathy S.; Evans, Mathew J.; Bandy, Brian J.; Monks, Paul S.; Edwards, Gavin D.; Phillips, Gavin (2002-12-11). "Potential for photochemical ozone formation in the troposphere over the North Atlantic as derived from aircraft observations during ACSOE". Journal of Geophysical Research: Atmospheres. 107 (D23): ACH 14–1–ACH 14–14. Bibcode:2002JGRD..107.4707R. doi:10.1029/2002jd002415. ISSN 0148-0227.